This application is based on Japanese Patent Application No. 9-66796 filed on Mar. 19, 1997, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a glass substrate structure and its manufacture method, and more particularly to a laminated glass substrate structure suitable for a display device or the like and its manufacture method.
b) Description of the Related Art
A glass substrate has the characteristics that it is hard and not susceptible to scratches and that a transparent glass substrate can be manufactured easily. By positively utilizing these characteristics, a glass substrate is used for forming various types of windows and display panels. For example, a liquid crystal display (LCD) is formed by laminating a pair of glass substrates and injecting liquid crystal into liquid crystal cells formed in between the pair of glass substrates. A plasma display panel (PDP) also uses a similar laminated glass substrate structure.
A glass substrate of a desired size is formed from a large plate glass by scribing the surface with a diamond cutter or the like and cleaving it by applying a bending stress. For example, in the manufacture of a liquid crystal display, a large plate glass is often cut into four pieces (generally called xe2x80x9cfour-plane cutxe2x80x9d). It is known that a cut plane of glass has very sharp edges. In order to avoid handling danger or in order to prevent the generation of glass chips at processes after cutting, it is also known to chamfer each edge of a glass substrate.
If foreign materials such as chips of glass substrates are mixed, a fatal defect such as pin holes may be formed in glass substrates of photomasks or electronic devices such as LCD. It is known that micro cracks are formed in a glass substrate chamfered by mechanical grinding with diamond or the like and may generate fine particles. Various methods have been proposed in order to prevent the generation of fine particles from a glass substrate.
One problem associated with a glass substrate is that it is heavier than a plastic plate or the like. A glass substrate structure, particularly a laminated glass substrate structure with a pair of glass substrates adhered together, is likely to become heavy. A laminated structure often becomes thick. Using a thin glass substrate has been desired in order to thin and lighten LCDs and PDPs. However, a thin glass substrate is easy to be broken. It is desired that cracks and breaks are not formed if an applied pressure is within a predetermined range, although this range depends on application fields of glass substrates.
For example, consideration should be paid to the fact that a user often presses the display surface of LCD. It is required that a laminated glass substrate structure of LCD is not broken even if a pressure within a certain range is applied to the display surface.
In a laminated glass substrate structure of LCD, a resistance to pressure applied to the structure in one direction is required to have a certain value or larger, as described above. However, techniques for improving such a load resistance of a glass substrate are not know to date.
It is an object of the present invention to provide a laminated glass substrate structure with an improved load resistance.
It is another object of the present invention to provide a method of manufacturing a laminated glass substrate structure capable of improving a load resistance.
According to one aspect of the present invention, there is provided a laminated glass substrate structure comprising: a first glass substrate having first and second main faces, all edges excepting one edge among edges defining the first main face having been subjected to a smoothing process;
and a second glass substrate having third and fourth main faces, two edges among edges defining the fourth main face not subjected to the smoothing process, the second glass substrate being adhered to the first glass substrate with a space formed therebetween and with the third main face facing to the second main face.
According to another aspect of the present invention, there is provided a method of forming a laminated glass substrate structure, comprising the steps of: a) preparing a first glass substrate having first and second main faces; b) preparing a second glass substrate having third and fourth main faces; c) after the steps a) and b), adhering the first and second glass substrates with a space formed therebetween and with the third main face facing to the second main face; and d) after the step c), performing a smoothing process relative to all edges excepting one edge among edges defining the first main face. The laminated glass substrate structure provides an improved load resistance. According to the experiments made by the present inventors, as a pressure is applied to one surface of a laminated glass substrate structure, first break occurs in a glass substrate on the side opposite to the glass substrate applied with the pressure. A break of a glass substrate mainly occurs in a surface applied with a tensile stress.
It has been found that a glass substrate having edges with micro cracks or chips and applied with a static load breaks by extending a crack or chip on one side to another one on another side. Namely, if a glass substrate has cracks or chips on only one side, the glass substrate is hard to be broken.
The load resistance of a glass substrate can therefore be improved by performing the smoothing process for edges excepting one among all edges defining the first main face applied with a largest tensile stress.
All the edges may also be subjected to a smoothing process or processes.
The smoothing process improves a resistance to a static load to be applied by a user of a laminated glass substrate so that it is sufficient if this process is performed after a pair of glass substrates is adhered. A pair of glass substrates is often adhered together by making at least two sides flush with each other. In such a case, if the smoothing process is performed for the flushed two sides of one of the substrates required of a higher load resistance, the smoothing process is often performed also for two sides of a glass substrate which is less required to be made resistant to a static load.
As above, the load resistance of a laminated glass substrate can be improved.